The structure of the pygmy dipole resonance has been investigated in the nuclei 140Ce, 138Ba, 124Sn, and 94Mo by performing experiments using different probes. On the one hand, real-photon scattering experiments have been conducted using the nuclear resonance fluorescence (NRF) method. On the other hand, α-scattering experiments have been done using the (α, α′, γ) coincidence technique. An unexpected difference in the excitation cross sections of the dipole strength below the particle threshold has been observed. While a group of PDR states could be excited in both kinds of experiments, a group of energetically higher-lying states could only be excited in NRF. In order to understand this phenomenon, theoretical calculations using the quasiparticle-phonon model (QPM) and the relativistic quasiparticle time-blocking approximation (RQTBA) have been performed for the nucleus 124Sn. A possible explanation for the observed splitting was found.
|Conference||Fourteenth International Symposium Guelph, Canada, 28 August – 2 September 2011|
|Period||28/08/11 → 2/09/11|